Method of treating acrylonitrile synthetic fiber

ABSTRACT

A method of treating acrylonitrile synthetic fibers which involves preparing a solution of acrylonitrile polymer containing -SO3M or -OSO3M and at least 80 percent by weight of acrylonitrile in said polymer which is dissolved in an aqueous solution of the salt of thiocyanic acid, wet spinning said solution in water of a dilute aqueous thiocyanate solution, treating said fiber with an aqueous solution of the inorganic salt of alkali metal atoms or an ammonium salt at a pH of 2.2 to 4.0 to combine from 75 to 95 percent of said groups in the fiber with the alkali metal atoms or ammonium ions, and finally washing said fiber with water.

United States Patent Inventors Kazuml Nakagawa;

Keitaro Shimoda; Kelliro Kuratani, all of ii Japan Appl. No. 857,653 Filed Sept. 11, 1969 Patented Nov. 23, 1971 Assignee Japan Exlan Company Limited O k J p Priority Oct. 27, 1965 Japan 40/66245 Continuation of application Ser. No. 588,282, Oct. 21, l966,'now abandoned. This application Sept. 1 l, 1969, Ser. No. 857,653

METHOD OF TREATING ACRYLONITRILE SYNTHETIC FIBER 1 Claim, No Drawings 1 1111.11 Dom/0o, D06p 5/00 Field of Search 8/1375,

Primary Examiner-Jay H. Woo Attorney-Wenderoth, Lind & Ponack ABSTRACT: A method of treating acrylonitrile synthetic fibers which involves preparing a solution of acrylonitrile polymer containing -SO M or -OSO;M and at least 80 percent by weight of acrylonitrile in said polymer which is dissolved in an aqueous solution of the salt of thiocyanic acid, wet spinning said solution in water of a dilute aqueous thiocyanate solution, treating said fiber with an aqueous solution of the inorganic salt of alkali metal atoms or an ammonium salt at a pH of 2.2 to 4.0 to combine from 75 to 95 percent of said groups in the fiber with the alkali metal atoms or ammonium ions, and

finally washing said fiber with water.

METHOD OF TREATING ACRYLONITRILE SYNTHETIC FIBER This is a continuation of Ser. No. 588,282 filed Oct. 21, 1966, and now abandoned.

The present invention relates to a method of producing an acrylonitrile synthetic fiber by the wet-spinning technique, and particularly, to a method of improving dyeability and stability in whiteness of an acrylonitrile synthetic fiber containing dissociable acid groups in the polymer chains, said improvement being effected in the course of spinning said fiber. It is by now a common knowledge to those skilled in the art to improve the dyeability or afiinity of an acrylonitrile synthetic fiber to basic dye by introducing into said fiber such acid groups as carboxylic and sulfonic groups, the introduction of such acid groups being effected by permitting acrylonitrile to copolymerize with unsaturated monomers containing carboxylic acids, e.g., acrylic acid, methacrylic acid, itaconic acid, maleic acid, etc., or unsaturated monomers containing sulfonic groups such as styrenesulfonic acid, vinylsulfonic acid, allylsulfonic acid, and methallylsulfonic acid, etc.

However, even in the case of acrylonitrile copolymers with unsaturated monomers containing no acid group, it is still possible to introduce sulfonic or carboxylic groups at the terminate of the polymer chains in so far as the copolymerization reaction is carried out in the presence of a catalyst system containing persulfuric acid, sulfurous acid, thiosulfuric acid, pyrosulfurous acid, oxalic acid, or some other acids.

It is found, however, that such an acrylic fiber containing dissociable acid groups in the polymer cannot be successfully dyed with certain dispersed dyes and cationic dyes, for the expected shade is not always obtained. The hues of the dyes change, presumably when the dyes combine with the dissociable acid groups.

In addition, acrylic synthetic fibers which are mostly resistant to acids but not to alkalies, tend to discolor yellowishbrown in alkaline media. Thus, acrylic synthetic fibers have the disadvantage that, when repeatedly exposed to alkaline media, such as in laundering, gradual discoloring in a yellowish-brown cast takes place. This discoloration in alkalies is generally believed to be caused by formation of conjugated double bonds-which is the ring formation of nitrile groups in the acrylonitrile polymer. It has been found that, when such dissociable acid groups as mentioned above are contained in the polymer forming the fiber, said alkali discoloration is greatly accelerated. Japanese Patent Publication No. 3895/52 of Sept. 26, 1952, described a method of manufacturing fibers having excellent whiteness which will remain unaffected by exposure to light and heat, by treating swollen and moisted acrylic fiber with an acidic medium at pH 5.8 or lower after extrusion and washing steps. It should be noted, however, that although whiteness of an acrylonitrile synthetic fiber may be enhanced by such a method as described in the patent, the whiteness of the fiber gradually decreases as the fiber is repeatedly laundered, namely not stable in the original fiber whiteness. Furthennore, the fiber produced in the manner described in the patent cannot be dyed into a reproducable shade if certain dispersed or cationic dyestufis (e.g., Sevron Orange L, E.l. DuPont, U.S.A).) are employed.

The Japanese Patent Publication No. 5273/62 of June 20, 1962, provides another method for manufacturing an acrylonitrile synthetic fiber, describing a wet-spun acrylonitrile synthetic fiber, while it is still moist, is treated with an aqueous solution of water-soluble alkali metals so as to improve the aifinity of said fiber for basic dyestuffs. According to this method, an acrylonitrile polymer is dissolved in a concentrated aqueous solution of thiocyanate and the resulting solution is extruded in water or a dilute aqueous solution of thiocyanate. When the extruded fiber is treated in the manner of the patent, dissociable acid groups contained in the polymer are linked with the metal ions, with a result that, although the fiber may be properly dyed to expected shades even with said types of dispersed or cationic dyes, its original whiteness is considerably inferior, accordingly with little prac tical value, to that of the fiber which has been treated according to the aforesaid Japanese Patent Publication No. 3895/52.

It is thus a primary object of the present invention to provide a method for manufacturing an acrylonitrile synthetic fiber which is properly dyeable to the initially expected shade with any dispersed or cationic dyestuffs.

In addition, the present invention provides an acrylonitrile synthetic fiber. possessing an excellent whiteness. Another object of the invention is to provide a method for manufacturing an acrylonitrile synthetic fiber, the improved whiteness of ment selected from the group consisting of H, alkali metals and ammonium ions, particularly in a concentrated aqueous thiocyanate solution, extruding the resulting solution in water or a dilute aqueous thiocyanate solution by means of the wetspinning technique, then treating the resulting fiber, while it is still moist, with an acid aqueous solution containing a colorless water-soluble alkali metal salt or ammonium salt, and finally wahing the fiber with water.

More particularly, the moist swollen fiber freshly extruded by the wet-spinning technique is first washed with water thoroughly until the thiocynate is substantially completely removed and, then, the fiber is further treated with a colorless aqueous solution which, dissolving alkali metal salt or ammonium salt, has been previously adjusted to pH 2.2-pH 4.0 and preferably pH3.0-pH 3.5, with organic or inorganic acid, at the solution temperature of 0-50 C., whereby at least 75 percent, preferably, from 75 percent to percent in mole percent of the dissociable acid groups in said fiber arecombined with the metal ions or ammonium ions. Lastly, the free alkali metal salt or ammonium salt absorbed on the fiber, as well as the inorganic or organic salt, is completely removed by washing the fiber with water.

Unless, in the above-mentioned treatment, 75 percent or more by mole of said alkali metal or ammonium ions are associated with the dissociable acid groups in said acrylonitrile synthetic fiber, it is impossible to dye the fiber to the proper shade with certain dispersed or cationic dyes. Conversely, should more than 95 percent by mole of said alkali metal or ammonium ions be combined with the acid groups, the whiteness of the fiber would be adversely affected.

To ensure that from 75 to 95 percent by mole of dissociable acid groups contained in the fiber be combined, as above, with the alkali metal or ammonium ions, it is sufficient to select the concentration of said alkali metal salt or ammonium salt in the treating bath within the range of 0.003 to 0.071 gram-ions per liter, and maintain the pH of the treating bath within the range of pH 2.2 to pH 4.0.

Since whiteness of the fiber, especially its intrinsic whiteness, will be rather impaired if the fiber is merely treated with the above-mentioned aqueous solution of alkali metal salt or ammonium salt, it is necessary to add an organic or inorganic acid as above to maintain the above-mentioned aqueous solution of alkali metal or ammonium salt within the range of from pH 2.2 to pH 4.0 and preferably from pH 3.0 to pH 3.5. Thus, if the pH of said solution exceeds pH 4, the absorbed ions of said alkali metal or ammonium ions on the dissociable acid groups of the polymer is increased to the extend that the intrinsic whiteness of the fiber is decreased. Conversely, with the aqueous solution being below pH 2, the absorbed ions of alkali metal or ammonium is so low that neither will the fiber be dyed to the proper shade with certain dispersed and cationic dyes nor the stability ofwhiteness will be obtained on -the resulting fiber. It is also unwise to employ a temperature beyond 50 C., for the fiber treated at such a high temperature could lose its transparency.

Furthermore, the fiber treated as above with the acidic aqueous solution of alkali metal salt or ammonium salt must be washed with water so as to completely remove not only the free alkali metal salt or ammonium salt absorbed on the fiber 'but also the acid employed. Thus, when the fiber contains residual amounts of said alkali metal or ammonium salt and said acid, both the intrinsic whiteness and transparency of the fiber is impaired as it is stretched in hot water and, moreover, the stability of whiteness of the final product is also affected.

Thus, as explained above, if the dissociable acid groups of an acrylonitrile synthetic fiber are available in the acid form, the fiber will not be dyed to the proper shade with certain dispersed or cationic dyes and the whiteness of the fiber will also be unstable, but if from 75 to 95 percent of the dissociable acid groups are combined with alkali metal or ammonium ions according to the present invention, the fiber will become dyeable to the proper shade with certain dispersed and cationic dyes and, at the same time, both its intrinsic whiteness and stability of the whiteness will be improved.

in carrying the present invention into practice, it is undesirable to employ a divalent or trivalent metal salt, for it will reduce the affinity of the fiber for dyestuffs. The present invention is particularly useful when it is embodied in conjunction with the wet-spinning technique, which consists of dissolving an acrylonitrile polymer in a concentrated aqueous solution of the salt of thiocyanic acid and extruding the resulting solution in a dilute aqueous solution of thiocyanate. The thiocyanate mentioned above may be selected from the class consisting of sodium thiocyanate, potassium thiocyanate, as well as various mixtures of said thiocyanates. The acrylonitrile synthetic fiber that is employed in this invention is, as aforesaid, a fiber containing 80 percent or more by weight of acrylonitrile and, in addition, dissociable acid groups. So far as these two conditions are satisfied, it may be of any form that is known as the acrylonitrile-type synthetic fiber, regardless whether it is made up of a copolymer of a blended polymer. It is, however, the most preferable in the case of copolymers containing sulfonic groups, whereby the sulfonic groups are introduced preferably by copolymerizing acrylonitrile, or acrylonitrile blended with other copolymerizable monolefins, with a monomer which is copolymerizable with acrylonitrile and contains sulfonic groups such as alkenyl aromatic sulfonic acid, vinylsulfonic acid, allysulfonic acid, metallylsulfonic acid, etc. The copolymerizable monoolefins mentioned above include, for example, acrylic esters such as methyl acrylate, ethyl acrylate, butyl acrylate, etc., methacrylic esters such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, etc., methacrylonitrile, vinylchloride, vinylidene chloride, acrylamide, methacrylamide, methyl vinyl ketone, vinylcarboxylates such as vinyl acetate, vinylpropionate, etc., N- methylolacrylamide, styrene, and methylstyrene.

The above-mentioned inorganic or organic acids that are to be employed according to this invention are water-soluble acids, such as sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, formic acid, acetic acid, oxalic acid, etc. The alkalimetal salts or ammonium salt mentioned hereinbefore may be selected from the class consisting of the watersoluble salts such as sulfates, nitrates and chlorides as typical examples which have potassium, sodium, lithium, and ammonium, etc. as cationic ions. The phrase certain dispersed dyes and/or cationic dyes" as used throughout this specification includes, for example, such dispersed dyes as paminoazobenzene, Cellitone Blue Extra, Cellitone Fast Orange GR, Cellitone Fast Red GG, Cellitone Blue Disarge Blue 36 (Berdische Aniline and Soda Fabriken, Germany), Chibaset Safric Blue G, Chibaset Orange GR (Ciba Limited, Switzerland), Dia Cellitone Brown R, Dia Cellitone Brown G,

Dia Cellitone Brown GF, Dia Cellitone Fast Gray G, Dia Cellitone Fast Orange GL, Dia Cellitone Brilliant Brown G, Dia Cellitone Brilliant Blue B (Mitsubishi Chemicals and Industries, Ltd.), etc., and such cationic dyes as Sevron Orange L, Sevron Brilliant Red 38 (SJ. DuPont, USA), etc. Many other dyes, of course, may also be included in this category.

'l'he follawi ng ekzin'lbies are given only for the purpose of describing the present invention in more detail and should be no means be construed as limiting the scopes of the invention. These examples, in which all parts and percents are by weight unless otherwise specified, illustrate preferred procedures based on the principles of the invention.

EXAMPLE l in this example, the dyeing operation and the measurement of the yellowness of fiber (as a reversed scale for whiteness) were carried out as follows:

Dyeing procedure Dye P-arninoawbenzene 0.3% owf Auxiliary agent Monogen S (Daiichi Kogyo Seiyaku K,K.) 2.5% owf Liquor ratio l:l00

The fiber was immersed in a dye bath at f C. under the conditions, said temperature being then raised up to 100 C. in 45 minutes. After 60 minutes of dyeing at 100 C. the bath was gradually cooled to 50 C.

Yellowness The filaments were aligned in the same direction and, then light reflection at wave lengths 453 mu, 553 my, and 595 mu were determined on the mass of the filaments as reference to a magnesium oxide disc. The yellowness of the fiber was then calculated by the following equation:

Yellowness R595 R453 [R553 X100 wherein R453, R553 and R595 respectively represents the reflection at wavelengths 453 mp.-553 mp, and 595 mg.

The smaller the value calculated as above, the more satisfactory the whiteness of the fiber.

The laundry conditions that are employed to determine the stability in whiteness of a sample fiber are as follows. The fiber is immersed in an aqueous solution containing 0.1 percent sodium metasilicate and 0.1 percent of Marcel soap, and dried at 98 C. for 30 minutes (bath ratio: l/20). The dried fiber is washed with water, dehydrated, and finally dried at C. for 10 minutes. This cycle is repeated seven times. The treated fiber is designated as a laundered fiber.

An acrylonitrile polymer composed of 91 parts of acrylonitrile, 9 parts of ethyl acrylate, and 0.3 part of sodium methallylsulfonate is dissolved in a 48 percent aqueous solution of sodium thiocyanate, and the resulting solution is extruded in an 8 percent aqueous solution of sodium thiocyanate. The tow of the extruded filaments is washed with water until the sodium thiocyanate is completely removed from the fiber, and then is further passed through an aqueous bath containing nitric acid and sodium sulfate (see Table 1). After the treating solution absorbed on the fiber bundle is completely removed by washing, the fiber is drawn in hot water at C. to eight times its initial length. After processed through steps such as drying heat-treatment, etc., the two are finally dried. Such fibers were dyed with paminoazobenzene, which is a dispersed dye. The results, as well as the degrees of intrinsic whiteness and of the postlaundry whiteness of these fibers, are summarized in table 1 TABLE 1 Treating bath Dyed fiber Yellowness Cone. of Original sodium Dominant (Na) not washe sulfate, wavelength, X1 After after the gel gram ion/l. m Shade .(SO H Original laundry treatment 580 Yellow 105 4. 5

( 594 Orange 70 2. 5 ll.

0. 0036 590 Golden 82 2. 9 9.

yellow 0. 0071 585 Yellow 85 3. 2.

( 596 0range 67 0. 8 l4.

0. 0142 590 Golden 84 2. 2 10.

yellow 0. 071 585 Yellow 82 3. 2 9. 579 ..-do 107 6.0 1. 0

\ Not added.

It is apparent from table 1 that, in case no sodium sulfate is added, the lower the pH of the bath, the higher the degree of intrinsic whiteness of the fiber, but the whiteness of the fiber after laundering is definitely inferior, that is to say, its whiteness is unstable. Moreover, the fiber is not properly dyed and its shade is far from the expected shade. The proper shade of the fiber dyed with p-aminoazobenzene is yellow and its dominant wavelength is 5 80 mp. It will also be noticed that even if sodium sulfate is added to the treating bath, the intrinsic whiteness of the fiber is poor so long as the pH of the bath is high, although shade of the dyed fiber is proper. It is as shown in the table 1, satisfactory in both intrinsic whiteness and whiteness stability and on the shade of dyed fiber, only when the fiber is treated in a bath at pH 3 to 3.5 and a sodium sulfate concentration of 0.0036 to 0.014 gram-ions per liter, and the treated fiber is then washed with water to remove the acid and sodium sulfate substantially completely. Even after the fiber is treated in the bath, if it is transferred to the succeeding steps of the process without removing the free acid and sodium sulfate it has absorbed, the final fiber is low in intrinsic whiteness, as shown in the very right column of the table I What we claim is:

l. A method of treating an acrylonitrile synthetic fiber consisting essentially of preparing a solution of acrylonitrile polymer containing $0 M or -0SO;,M in which M represents a member selected from the group consisting of H, alkali metal atoms and ammonium ions and at least percent by weight of acrylonitrile in said polymer by dissolving said polymer in a concentrated aqueous thiocyanate, wet spinning said solution in water or a dilute aqueous thiocyanate solution, washing the fiber with water until the thiocyanate is substantially removed from the fiber, treating said fiber with an aqueous solution of the inorganic salt of alkali metal atoms or ammonium salts having a concentration of 0.003 to 0.071 gramions per liter at a pH of 2.2 to 4.0 to combine from 75 TO percent of said groups in the fiber with the alkali metal atoms or ammonium ions, and washing said fiber with water.

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